Assisting a driver to increase braking force applied to a vehicle is known. In particular, engine intake manifold vacuum is used within a brake booster to increase the force a driver applies to a brake pedal to actuate vehicle brakes. Vacuum in the brake booster is used to augment vehicle brake force each time the vehicle brake pedal is applied. However, boosted engines are sometimes operated where the engine intake manifold is at a positive pressure rather than a vacuum. Thus, it may be difficult to provide vacuum to the brake booster to assist the driver under some operating conditions. Further, even when there is intake manifold vacuum, the intake manifold vacuum may not be present long enough for brake booster vacuum to recover internal vacuum such that the brake booster provides a desired amount of brake force augmentation to the driver the next time the vehicle brakes are applied.
The inventors herein have recognized the issues of vacuum assisted brakes in boosted engines and have developed an interconnection between the intake manifold and the brake booster that allows for an improved rate of vacuum recovery within the brake booster. By improving the vacuum recovery rate of the brake booster it may be possible to eliminate a vacuum pump on a boosted engine. However, improving a rate of vacuum recovery in a brake booster can also produce engine air amount disturbances (e.g., un-throttled air flow rate) as air is exchanged from the brake booster to the engine intake manifold. And, engine air amount disturbances can increase engine emissions and may be noticeable to the driver.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: adjusting an actuator to substantially maintain an engine intake manifold pressure in response to a brake booster to intake manifold flow rate when brake booster vacuum changes, the brake booster vacuum change in response to a change in a position of a brake pedal.
By adjusting an actuator in response to a brake booster to intake manifold flow rate, it may be possible to provide brake booster vacuum while limiting engine emissions and driver disturbances. For example, a driver may repeatedly accelerate and brake a vehicle during the course of driving. When the driver releases the throttle to brake there may be a brief opportunity to recharge the brake booster with vacuum. If the engine throttle is adjusted in response to a brake booster to intake manifold flow rate, the intake manifold pressure rate of change may be limited or substantially maintained at a constant pressure so that changes in engine operation are mitigated. In one example, an intake throttle can be closed (e.g., partially or fully) when the brake booster is replenished with vacuum from the intake manifold. In this way, the throttle position is adjusted to compensate for flow from the brake booster.
The present description may provide several advantages. For example, the approach may reduce system costs of a boosted engine by eliminating or reducing the size of a system vacuum pump. Further, the approach can improve engine emissions and reduce engine air disturbances when replenishing vacuum to a brake booster.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.